The purpose of this investigation is to identify how has been built and validated the knowledge in Physical Education in the school. The starting point is the analysis of school Physical Education programs in Uruguay (1923, 1986, 2005 y 2008). The conception underlying Physical Education and the possible relation with a specific knowledge of the field is tracked. This first analysis is combined with a profundization in two contents: sports and expressive activities, taking into account its historical development from a disciplinary analysis. Based on the initial assumption that the first one is an indisputable school content, and the second one is an innovation of the last official program. The methodology used was the analysis of documents, as well as interviews with teachers who participated in the preparation of the 2005 and 2008 programs.  
